In known live roller accumulator conveyors prior to our above U.S. Pat. No. 4,108,303, the primary driving means for the live rollers was an endless belt, from which the drive was transmitted to selected rollers by a plurality of power transmission devices mounted for movement between a driving position and a retracted position out of driving engagement with the belt or the driven rollers. Typical such accumulator conveyors are shown in Currie U.S. Pat. No. 3,225,893 and Wallis U.S. Pat. No. 3,612,248.
It has also been suggested to construct an accumulator conveyor wherein the primary driving means comprises an endless roller chain and sprockets which form parts of the power transmission devices. Such an accumulator conveyor drive is shown in Muller U.S. Pat. No. 3,718,248, but in Muller, the guides which support the driving run of the chain are fixedly mounted in spaced relation with the several power transmission devices, and there is no provision for mounting the chain in assured driving relation with the sprocket in each power transmission device.